Copolyesters derived from terephthalic acid and isophthalic acid with aliphatic diols having 2 to 12 carbon atoms are known as melt adhesives. In such compositions, it is also known to include aliphatic dicarboxylic acids. It has been found most desirable that, for such compositions, the melting point of the copolyester be between about 80.degree. and 150.degree. C. Such melt adhesive compositions are described in EP-A-78889, DE-A-1920432, DE-A-2937946, U.S. Pat. No. 3,699,921, U.S. Pat. No. 4,094,721, and WO-A-83/2621.
For example, U.S. Pat. No. 4,496,713 teaches copolyesters of terephthalic acid, butanediol, and other aliphatic diols having 6 to 20 carbon atoms. Such compositions are useful for injection molding or extrusion. However, the elevated melting points of these materials render them undesirable for use in connection with temperature sensitive substrates such as textiles.
In U.S. Pat. No. 4,094,721, there are taught copolyesters of terephthalic acid, isophthalic acid, butanediol, and hexane diol. Optionally, one or more saturated dicarboxylic acids having 4 to 34 carbon atoms may also be included. These materials, however, have a substantial tendency to agglomerate, especially on milling and storage (see U.S. Pat. No. 4,217,426). In addition, these compositions do not stand up to repeated washings at normal washing temperatures.
It is also known to prepare copolyesters from terephthalic acid, adipic acid, ethylene glycol, and butanediol (see DE-A-1920432). However, the materials described in the foregoing reference have softening points in excess of 130.degree. C., at which temperature things as temperature sensitive fabrics cannot readily withstand. If the composition is selected so that the softening point is below 130.degree. C., it is too sticky to be useful in preparation of powdered coating materials as described in U.S. Pat. No. 4,094,721.
Japanese 58-134 114 describes polyester hot-melt adhesives which are derived from terephthalic acid, isophthalic acid, butanediol, and an additional diol. The diols set forth have a maximum of 5 carbon atoms. There is no suggestion that a different carbon atom range would produce any improved results.
Copolyesters based on terephthalic acid, adipic acid, ethylene glycol, and butanediol are also disclosed in U.S. Pat. No. 3,669,921. The agglomeration tendency of such compositions is so great that it is necessary to introduce substantial amounts of highly dispersed silicon dioxide in order to permit the granulate to be milled. Moreover, silicon dioxide must also be added to obtain a powder which would be suitable for coating, as described in WO-A-83/2621.
The latter patent teaches the combination of terephthalic acid, butanediol, diethylene glycol, and at least one saturated dicarboxylic acid having 3 to 12 carbon atoms. However, it has been found that the resistance to washing of such compositions is unacceptable.
EP-A-78889 describes the combination of terephthalic acid, isophthalic acid, butanediol, an inorganic powder, and aliphatic diols having 5 to 12 carbon atoms. While these compositions do not exhibit the tendency to agglomerate or to have poor storage stability, nonetheless, they are not really satisfactory for the purposes of the present invention. More specifically, their resistance to washing and dry cleaning is extremely poor and tends to the formation of undesirable bubbles.
In summary, prior art compositions of this nature suffer from important drawbacks. These include tendency to agglomerate, difficulty in milling, and lack of resistance to repeated washings. The last generally manifests itself in the formation of bubbles which not only detracts from the smooth feel of the fabric, but also weakens the bond itself.